The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load.
In a healthy intervertebral disc, cells within the nucleus pulposus produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus within its cushioning qualities. These nucleus pulposus cells may also secrete small amounts of cytokines such as interleukin-1β and TNF-α as well as matrix metalloproteinases (“MMPs”). These cytokines and MMPs help regulate the metabolism of the nucleus pulposus cells.
In some instances of disc degeneration disease (DDD), gradual degeneration of the intervetebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased loads and pressures on the nucleus pulposus cause the cells within the disc (or invading macrophages) to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors or apoptosis can also cause the cells within the nucleus pulposus to emit toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to eliminate waste may result in the accumulation of high levels of toxins that may cause nerve irritation and pain.
As DDD progresses, toxic levels of the cytokines and MMPs present in the nucleus pulposus begin to degrade the extracellular matrix, in particular, the MMPs (as mediated by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing its water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the loading pattern within the disc, thereby possibly causing delamination of the annulus fibrosus. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, thereby upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain.
Two of the more common treatments of the herniated disc are the discectomy, total disc replacement and the fusion. In a discectomy, the surgeon removes the bulging disc material. In a fusion, the surgeon clears out a portion of the disc, inserts an intervertebral implant into the disc space. In each case, removal of disc material is an important step.
Automatic transportation of cut disc material has shown to be a significant challenge for automated disc removal tools, especially with small diameter tools designed for minimally invasive surgery. Auger designs have been shown to be very effective in terms of transportation. However, as flexibility and steerability are desirable in disc removal tools, transport augers should also be flexible.
U.S. Pat. No. 7,591,790 (“Pflueger”) discloses an apparatus for removing tissue and/or other material from a patient. The apparatus generally includes a handpiece and a tissue removal mechanism connected thereto. The tissue removal mechanism includes a cannula having an open distal tip and an outer diameter of less than about 5 mm, or less than about 2 mm. The mechanism further includes a rotatable element having a distal portion with helical threading. The distal portion of the rotatable element extends beyond the open distal tip of the cannula in order to allow tissue to prolapse between turns of the helical threading. The apparatus is designed to draw soft tissue into the cannula upon rotation of the rotatable element and without the need for supplemental sources of aspiration. The auger of the '790 patent design has a center axis that is solid, which means that the removed material is transported against the auger itself.
US 2013-0103067 (“Fabro”) discloses tissue removal devices, wherein the tissue removal device may comprise a handheld housing, a motor, and a tissue removal mechanism coupled to the handheld housing. The tissue removal mechanism may comprise a tubular member, a rotatable elongated member disposed within a lumen of the tubular member, a first impeller distal to the rotatable elongated member, and a second impeller adjacent the first impeller. Fabro discloses a discectomy device comprising a wire wrapped around a core.
U.S. Pat. No. 6,033,105 (“Barker”) discloses an integrated bone cement mixing and delivery system using an auger mechanism as the means for advancing the bone cement through the delivery chamber.